The present invention relates to a miniature display device which is electrostatically operated and which makes it possible to produce display cells which can be used in particular in battery-powered portable equipment such as electronic calculators and watches. The invention also concerns a process for producing the miniature display device.
Considerable efforts have been made to discover and develop display systems which are aesthetically pleasing, which operate with a low supply voltage, which have a very low level of power consumption and which can be produced inexpensively. Liquid crystal display devices fulfilled these conditions until the power consumption of electronic circuits, in particular CMOS-type integrated circuits, fell to such a point that the contribution of the display device to overall power consumption ceased to be negligible. Moreover, actuation of such devices is complex and the contrast and aesthetics thereof are not always among the best.
Among display devices which have a low level of power consumption, mention may be made of that which is known by the name "The Distec System" and described in the document "An Electrostatic Sign--The Distec System", W. R. Aiken, Display Technology Corp., Cupertino, Calif., U.S.A. This device is used as an advertising panel or sign of large dimensions. It comprises modules formed by shutter members which are suspended at one axis by hinge members and which are capable of rotating under the effect of an electrical field applied by a system of electrodes. The control voltage is approximately 3000 volts. However, it has never been suggested that this system might be adapted to provide a miniature display with a low control voltage.
Light modulating devices are also know, which use diaphragms which are deformable under the influence of an electrical field or an electron beam and which can be produced by means of methods derived from the production of integrated circuits. Such modulating devices are described for example in U.S. Pat. Nos. 3,600,798 and 3,886,310. The first patent discloses a device which makes it possible to modulate the amount of light transmitted by deformation of a diaphragm or membrane under the influence of an electrical field, while the second patent describes a device which makes it possible to modify the angle of reflection of the light, by deformation of a diaphragm under the effect of an electron beam. However, neither of these devices is a display device, the amplitude of the movement of the diaphragm in both cases being very small and the provision of an additional light source being necessary.